Pullbox Sizing

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Jason Spray

Member
Location
Phoenix, AZ USA
I have an installation where (3) 4" EMT conduits will be entering a pullbox from the bottom, and exiting out the back (at the top)
Assuming that I'm correct that since the conductors don't exit directly across from each other, the calculation would be (6x4")+4"+4" = 32" so a 32" x 32" box.
My real question is concerning the depth of the pullbox. Do I use Table 312.6(A) to calculate the depth? I am installing (4) 400kCMIL, so I see that as 12". Is that correct?
My next concerns is that I read an article by Mike Holt in EC&M (http://www.ecmweb.com/code-basics/sizing-junction-boxes) and he indicates that when conductors enter an enclosure with a removable cover, the distance from the removable cover to where the conductors enter must mot be less that the bending radius listed in Table 312.6(A) based on one conductor per terminal. So 6" should be deep enough?
The size of my pullbox should be 32"x32"x6" correct?
 
shboal11

shboal11

Member
Location
Grand Terrace, California
Jason Spray said:
I have an installation where (3) 4" EMT conduits will be entering a pullbox from the bottom, and exiting out the back (at the top)
Assuming that I'm correct that since the conductors don't exit directly across from each other, the calculation would be (6x4")+4"+4" = 32" so a 32" x 32" box.
My real question is concerning the depth of the pullbox. Do I use Table 312.6(A) to calculate the depth? I am installing (4) 400kCMIL, so I see that as 12". Is that correct?
My next concerns is that I read an article by Mike Holt in EC&M (http://www.ecmweb.com/code-basics/sizing-junction-boxes) and he indicates that when conductors enter an enclosure with a removable cover, the distance from the removable cover to where the conductors enter must mot be less that the bending radius listed in Table 312.6(A) based on one conductor per terminal. So 6" should be deep enough?
The size of my pullbox should be 32"x32"x6" correct?
Click to expand...
By my calculations you are correct

Sent from my SM-G930V using Tapatalk
 
Smart $

Smart $

Esteemed Member
Location
Ohio
The box is not required to be 32" wide. It only has to be wide enough to accommodate the (3) 4" entering the bottom and (3) out the back.
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Here is a good graphic compliments
enhance
of mike holt
 
C

Carultch

Senior Member
Location
Massachusetts
infinity said:
Shouldn't there be a minimum distance between the two raceways in the box?
Click to expand...

I was just thinking the same thing. Should the 6X rule apply to the distance between raceway entries? Or should the 6X rule apply to the total size of the box? Both questions applying to the case of a side-to-back pull.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Carultch said:
I was just thinking the same thing. Should the 6X rule apply to the distance between raceway entries? Or should the 6X rule apply to the total size of the box? Both questions applying to the case of a side-to-back pull.
Click to expand...
Both requirements have to be met. If this were just one in, one out, the height of the box would have to be over 7x if it were vertically narrow... 6x for between raceways and 1x for the back raceway.

However, given this case has (3) in a row across the bottom, the extra 2x should be enough to allow the back raceways to be installed at the top and provide 6x distance in between.
 
W

wireman

Inactive, Email Never Verified
I did not see the wire size mentioned here and that may be the real determining factor for how big and deep it should be.

Sheet metal is cheap these days compared to labor $$ and skinned knuckles. If your physical layout allows a larger box then by all means use up the space.

Just my opinion.
 
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